Field
The present invention relates to display devices including light-emitting diode (LED) based backlight units (BLUs) and phosphor films including luminescent nanocrystals such as quantum dots (QDs).
Background
Display devices (e.g., liquid crystal displays (LCDs)) are used as screens or displays for a wide variety of electronic devices and typically require some form of backlighting for images to be visible in normal or reduced ambient light environments. In a BLU of the display device, LEDs are typically utilized as a light source. The LEDs may be arranged in a two dimensional array behind the viewing area of the display device or around the edge or perimeter of the display device. The BLU may also utilize phosphors, such as yttrium-aluminum-garnet (YAG) phosphors.
Luminescent nanocrystals represent a new, alternative class of phosphors often used in configurations where the phosphor may be placed external to the LEDs. Light emanating from the LEDs may be processed through a phosphor film of the display device to produce white light, which may be distributed across a display screen of the display device.
For example, luminescent nanocrystals may be embedded in a flexible film/sheet (e.g., quantum dot enhancement film (QDEF®) supplied commercially from 3M Company, St. Paul, Minn. using quantum dots supplied by Nanosys, Inc, Milpitas, Calif.) that may be placed in the display device (see, e.g., U.S. Patent Publication Nos. 2010/0110728 and 2012/0113672, which are incorporated by reference herein in their entirety). QDEF is a registered trademark of Nanosys, Inc. In other examples, luminescent nanocrystals may be encapsulated in a container, for example a capillary (see, e.g., U.S. Patent Publication No. 2010/0110728).
In current display devices using QDEFs, the white point values of the light distributed across display screens depend on the QD population size in the QDEFs. The QD population size can be adjusted by changing the concentration of QDs in the QDEF and/or changing the thickness of the QDEF. Furthermore, reducing the QD population size in order to achieve a given white point can reduce the cost of display devices using QDEF. However, maximum thickness of QDEFs may be limited by the thickness of display devices and maximum QD concentration may be limited by current technology. These limitations can present challenges in achieving the white point values specified by manufacturers and/or reducing the cost of display devices.